To improve a channel capacity and communication quality of a communications device, a conventional single-input single-output (Single-Input Single-Output, SISO for short) antenna in the communications device may be replaced with a multiple-input multiple-output (Multiple-Input Multiple-Output, MIMO for short) antenna. Compared with the conventional SISO antenna that has one antenna unit, the MIMO antenna may include a plurality of antenna units. The MIMO antenna receives and transmits information by using the plurality of antenna units, so that the channel capacity and the communication quality can be improved.
In the MIMO antenna, mutual coupling between the plurality of antenna units causes mutual interference between the plurality of antenna units. To avoid the interference between the antenna units, a distance between the antenna units may be made greater than a preset distance, thereby implementing decoupling between the plurality of antenna units. However, as sizes of antennas are becoming smaller, the distance between the antenna units is restricted, and consequently, the coupling between the antenna units cannot be eliminated. In a common MIMO antenna, for a fixed frequency band, a neutralization line corresponding to the fixed frequency band may be disposed between neighboring antenna units in the plurality of antenna units, so as to neutralize a coupling current between the neighboring antenna units by using the neutralization line, thereby implementing decoupling of the antenna units. With development of multiband multimode communications, a MIMO antenna supporting multiband multimode communications emerges. That is, the MIMO antenna can support a plurality of frequency bands.
However, a problem of coupling between antenna units of the MIMO antenna supporting a plurality of frequency bands still cannot be resolved.